1. Field of the Invention
The present invention relates to an organic electroluminescent (hereinafter referred to as “EL”) display technique.
2. Description of the Related Art
Flat-panel displays, typified by liquid crystal displays, are lower in profiles and power consumptions and lighter in weights as compared with CRT (cathode-ray tube) displays. By virtue of such characteristics, the demand for flat-panel displays has been growing sharply. For example, flat-panel displays are utilized as the displays of portable and stationary devices.
Organic EL displays are self-emission displays, thus are advantageous in achieving a higher response speed, wider viewing angle, higher contrast, lower profile and lighter weight as compared with liquid crystal displays. For this reason, organic EL displays have been studied actively in recent years.
An organic EL display includes an organic EL element. The organic EL element includes an anode, a cathode, and an emitting layer interposed therebetween. In the emitting layer, recombination of holes from the anode and electrons from the cathode occurs. As a result, the emitting layer emits light.
An organic EL display can display a full-color image when such a structure is employed that organic EL elements different in luminescent colors from one another are arranged. For example, a full-color image can be displayed on the organic EL display in which pixels of red, green and blue luminescent colors are arranged.
When such a structure is employed, it is necessary in manufacturing an organic EL display to form patterned emitting layers whose emitting colors are red, green and blue. For example, when low molecular-weight substances are used as the materials of the emitting layers, each patterned emitting layer is formed by vacuum evaporation using a fine metal mask as described in JP-A 2003-157973 (KOKAI).
In this method, however, higher the definition or resolution, greater the effect of the position accuracy on the display quality becomes. For example, when the sizes of pixels are small, the color mixture is prone to occur. This is because the fine metal mask used in vacuum evaporation is lower in accuracies of pattern shape and pattern size than the photomask used in photolithography and the fine metal mask expands or is deformed due to the radiant heat from the evaporation source in contrast to the photolithography using the photomask.
This problem is more serious when the fine metal mask is large. Thus, when emitting layers are formed using fine metal masks, organic EL displays, in particular, oversized organic EL displays are difficult to manufacture at high yields.